Elephants’ ancestors constantly migrated due to climate change

By Stephen Beech

Ancestors of today's elephants were forced to constantly migrate because of climate change, new research reveals.

Analysis of ancient DNA from the remains of mastodons - including those which roamed along the Pacific and Atlantic coasts of North America - has revealed the Ice Age giants migrated "vast distances" in response to shifting weather patterns.

The study, published in the journal Science Advances, provide new evidence which significantly revises and reshapes previous understanding of the species’ evolutionary history.

Well-preserved fossilized specimens of teeth, tusks and bone - dating back hundreds of thousands of years -together with new scientific techniques, allowed researchers from McMaster University in Canada and Harvard University in the US to rebuild genomes from tiny DNA fragments.

The team reconstructed the mitochondrial genomes from five mastodon specimens from Nova Scotia and the eastern seaboard and, for the first time, a unique specimen of a Pacific mastodon from Tualatin, Oregon, in addition to a partial mitochondrial genome from Northern Ontario.

The researchers explained that mastodons were initially split into numerous separate species, but later consolidated back into a single one - Mammut americanum.

More recently, that classification has been revised to potentially include at least two distinct species: the American and the Pacific mastodon (M. pacificus), although a debate over the split has persisted.

The new genetic analyses confirm the Pacific mastodons belong to a very old, well-established and separate genetic branch, with a range that extended much farther than previously believed - reaching deep into the Pacific Northwest, possibly south to Mexico, and as far north as Alberta.

The researcher say Alberta in present day Canada appears to have been a "hot spot" where Pacific and American mastodons congregated, expanded northward and may have interbred.

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The East Coast and Northern Ontario specimens revealed two new and distinct genetic groups, known as clades, of mastodons living in the same region but at different times.

The researchers say the eastern species were "surprisingly diverse" - arriving in distinct waves of migration at least three times, a pattern driven by repeated cycles of climate warming, leading to glacial melting and the opening of new territory for northward expansion.

When climate cooled and glaciers expanded, mastodons were driven south or went locally extinct.

Study senior author Professor Hendrik Poinar, director of the McMaster Ancient DNA Centre, said: “The data shifts our view of the region today known as Alberta and the north more generally, from a marginal roaming ground to a repeatedly occupied migratory corridor and significant landscape for mastodons with possible interbreeding."

The research team also pinpointed a mysterious and "genetically distinct" Mexican mastodon lineage, which they believe could be a deeper branch of the western species M. pacificus or possibly an entirely new, third mastodon species.

The mastodon was among the largest living land animals on Earth during the Ice Age, roaming from present-day Alaska and the Yukon east to Nova Scotia and south to Central Mexico.

Scientists say they were primarily browsers, living in swampy settings, eating shrubs and low-hanging tree branches, and occupied a very different habitant from their distant cousins, the Ice Age iconic woolly mammoths which roamed on open grasslands and tundra.

Study lead author Dr. Emil Karpinski, a research fellow at Harvard Medical School, added: “This study represents several firsts which includes our work on the Pacific mastodon.

"It also poses many new questions. For example, how did these distant species of mastodon interact in Alberta? Did they compete for resources, or did they interbreed as our lab has previously shown for mammoths?”

The researchers say their findings, combined with those from a 2020 study conducted by the same team, create a much more complete picture of how mastodons moved and diversified across North America.